Conventional radar devices typically use scan-to-scan correlation processing to remove unused signals, such as reflections from a sea surface (sea surface reflections), so that easy discrimination of the reflections from target objects is possible (for example, refer to JP 03-163383(A)). The scan-to-scan correlation processing includes comparing latest-acquired echo data with echo data for several scans of the past, and generating display data based on the temporal behavior of the echo data. As for the reflection signals from a target object, such as a vessel or land, they are highly stable so that their echo data appear in the same pixel; however, the sea surface reflection signals are less stable so that their echo data do not appear easily in the same pixel. Thus, the scan-to-scan correlation processing utilizes this difference to distinguish the reflection signals from the target object and the sea surface reflection signals.
Meanwhile, because an area where rain/snow reflection signals occur is usually relatively large and a moving speed of the occurring area is slow, the rain/snow reflection signals remain in the same pixels over a long period of time. Therefore, the rain/snow reflection signals are highly stable similar to the reflection signals from the target object so that their echo data appear continuously in the same pixels. For this reason, it is difficult for the conventional scan-to-scan correlation processing to display the rain/snow reflections which are unused images while suppressing them.
There exists FTC (First Time Constant) processing and CFAR (Constant False Alarm Rate) processing as techniques for suppressing the rain/snow reflection signals. These processing reduce the intensity of the rain/snow reflection signals; however, at the same time, they reduce the intensity of the reflection signals from a land which extends in the distance direction from the radar.